Polyetheretherketone (PEEK) retaining ring for an acetabular cup assembly

ABSTRACT

A prosthetic acetabular cup assembly, for receiving a ball attached to a femur, including components interlocked via a locking mechanism that includes a retaining ring fabricated at least in part using a polyaryletherketone material, such as PEEK. The locking mechanism is designed to meet predefined constraints such as assuring that substantially all motion is eliminated between assembled parts, assuring further that push-in/pull-out forces of assembly are within generally accepted industry standards, etc. Further aspect of the invention are directed to (a) the form and composition of the locking mechanism per se, such as locking mechanisms including a retaining ring fabricated at least in part using a polyaryletherketone material, where the shape of the retaining ring and manner in which it cooperates with the other components in the cup assembly results in a locking mechanism that satisfies the aforementioned constraints; (b) processes for fabricating specific types of retaining rings for use in securing the components of an acetabular cup assembly; and (c) to locking rings per se made utilizing polyaryletherketone material and composites including a polyaryletherketone material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to hip prosthesis assemblies forreplacing a natural hip socket; the form and composition of lockingmechanisms used in such assemblies to secure the attachment of assemblycomponents; and to processes for fabricating specific types of lockingmechanisms, including retaining rings per se, contemplated by theinvention.

More particularly, a first aspect of the present invention relates to aprosthetic acetabular cup assembly for receiving a ball attached to afemur. The components of the assembly (an insert bearing component andan outer shell component, both to be described in greater detailhereinafter) are, according to a preferred embodiment of the invention,interlocked via a locking mechanism that includes a retaining ringfabricated at least in part using polyaryletherketone material, such asPEEK.

The locking mechanism used in such assemblies may take any one of anumber of shapes that are useful for securing assembly components.Constraints influencing locking mechanism design include insuring thatsubstantially all motion is eliminated between assembled parts, insuringfurther that push-in/pull-out forces of assembly are within generallyaccepted industry standards, etc.

A further aspect of the invention is directed to the form andcomposition of the locking mechanism per se. More particularly, variousspecific locking mechanisms, fabricated using polyaryletherketonematerial, have been identified which have been found to haveadvantageous shapes for meeting the aforementioned constraints. Forexample, according to one embodiment of the invention the lockingmechanism includes a hex-shaped retaining ring having an inside radialchamfer, where the retaining ring is a composite fabricated at least inpart using PEEK combined with a reinforcing material, e.g., carbonfiber, with the reinforcing material being added to the PEEK matrix inorder to reinforce the composite ring (e.g., to strengthen and addrigidity to the ring).

Still further aspects of the invention are, as indicated hereinabove,directed to processes for fabricating specific types of retaining ringsfor use in securing the components of an acetabular cup assembly; and tolocking rings per se made utilizing polyaryletherketone material.

2. Description of the Related Art

It is known to provide an acetabular cup assembly, including a metalshell component for attachment to an acetabulum, to replace the naturalsocket; and to provide a polymer bearing component which is insertedinto the shell to provide a hemispherical bearing surface for receivinga femur ball prosthesis element. Often, the polymer bearing component(also referred to herein as an "insert" component) is nonsymmetrical andincludes a built up lip around a portion of the hemispherical bearingsurface to help prevent dislocation of an installed femur ball from thehemispherical bearing surface.

During installation of the acetabular cup assembly, the shell componentis first secured to the acetabulum. When a surgeon installs the bearingcomponent, the surgeon selects an orientation of the bearing withrespect to the shell component to align the lip of the nonsymmetricalbearing component in the most advantageous position to reduce thelikelihood of dislocation of the femur ball.

Therefore, it is desirable to produce an acetabular cup assembly inwhich (a) the bearing component can be easily attached to the shellcomponent in a large number of selected orientations to provide themaximum degree of flexibility for the surgeon using only a push-in forcewithin some predefined range; and (b) the retention mechanism (forinterlocking the shell and insert, also referred to herein as the"locking mechanism") allows the bearing component to be easily orientedand easily installed (as indicated hereinbefore); and easily removed bythe surgeon, if necessary, using only a pull-out force within somepredefined range.

The installed bearing component must also be secured to the shellcomponent by a retention force (and associated means for inducing suchforce) that is strong enough to prevent rotation or dislocation of thebearing component from the shell component when the cup assembly iscompleted and being used as intended as a hip prosthesis device, i.e.,after having been installed by the surgeon within the shell at thedesired orientation.

An example of prior art addressing some of the aforementioned desirableaspects of an acetabular cup assembly and locking mechanism therefore,is U.S. Pat. No. 5,049,158, issued on Sep. 17, 1991, to Engelhardt etal. U.S. Pat. No. 5,049,158 is hereby incorporated by reference.

The objectives of the incorporated reference (many of which are sharedby the present invention) included (a) providing a retention mechanismfor retaining a bearing component situated at any selected orientationinside a shell component which does not rely on the physical propertiesof the bearing component; (b) reducing the loading of forces on an outerlip or flange of the bearing component after the hip prosthesis isinstalled in a patient; (c) preventing rotation of the bearing componentrelative to the shell component after insertion of the bearing componentinto the shell component in a desired orientation; and (d) providing aself adjusting locking mechanism which retains the bearing componentinside the shell component despite possible shrinkage of the bearingcomponent after installation.

The incorporated reference met these objectives via its teaching of aprosthetic acetabular cup assembly that includes a single piece bearingcomponent having an inner bearing surface for receiving a ball attachedto a femoral prosthesis and an outer surface. The assembly includes ashell component for attachment to an acetabulum to replace a natural hipsocket and has an inner surface defining a cavity for receiving thebearing component therein.

According to the incorporated reference, a formed wire is situated in anarcuate groove that is part of the shell component. The formed wire isconfigured so that a portion of the wire extends radially inwardly fromthe arcuate groove of the shell component to engage a corresponding,axially aligned, arcuate groove formed in the bearing component toretain the bearing component inside the shell component without the useof attachment screws or the like.

Furthermore, according to the incorporated reference, anti-rotation lugsare formed on the inner surface of the shell component to cut into theouter surface of the bearing component as the bearing component isinserted into the shell component to prevent rotation of the bearingcomponent relative to the shell component.

The incorporated reference goes on to teach the use, according to apreferred embodiment of the invention taught, of a serpentine shapedlock wire to interconnect and lock together the aforementioned bearingand shell components; with the lock wire preferably being made of cobaltchrome material that is shaped by conventional wire forming techniques.The resulting metal wire is, according to the reference, optionally heattreated to increase its strength. Titanium is also suggested byEngelhardt et al. as an alternate metal for fabricating the lock wire.

U.S. Pat. No. 4,380,090, issued Apr. 29, 1983, to Ramos, is anotherexample of prior art which teaches the use of locking rings for anacetabular cup assembly. In particular, Ramos teaches that the lock ringfor an acetabular cup assembly is "preferably made of a resistant metalsuch as Vitallium or stainless steel".

Using metal wire rings as part of a locking mechanism for interlockingcomponents of an acetabular cup assembly, as taught in the prior artexemplified by the patents referred to hereinabove, is inherentlyproblematic. For example, as those skilled in the art will readilyappreciate, if the rings are made too thick they are stiff and not easyto work with; if the rings are made to thin they are "sloppy", that isthey do not always retain their intended shape, spring capacity, etc.

Further problems with locking mechanisms for acetabular cup assembliesthat employ metallic retaining rings include the prospect ofunacceptably high push-in and/or pull-out forces being required whenrespectively assembling or trying to purposely disengage assemblycomponents. For example, in the experiments to be described hereinafterit was found that a pull out force in excess of 1,500 pounds wasrequired for Vitallium (TM) rings of approx. 0.050" in diameter.

Further yet, use of metallic wire lock rings, such as the Vitalliumrings preferred by the aforementioned Ramos reference, etc., are knownto be problematic because of certain inherently difficult and/orexpensive process steps required when working with such material.Examples of such process steps include those steps needed to perform theinherently difficult task of converting straight wire into a desiredwavy structure; steps needed to heat treat metallic wire retaining ringsto increase their strength, etc.

Alternative materials for making lock rings, such as silicone andUltra-High Molecular Weight Polyethylene (UHMWPE), are also known in theart. However, many of these materials suffer from problems of their own.For example, both silicone and UHMWPE have inconsistent problems with awide spread of push-in and push-out strengths, problems related to theshell/insert interface being too loose when these materials are used tofabricate the retaining ring, etc. Several of these problems weredemonstrated in experiments referred to hereinafter, in the DetailedDescription of the invention, where polyethylene was used to fabricateexperimental retaining rings.

For all of the reasons set forth hereinabove, it would be desirable toprovide an acetabular cup assembly design which is easy to use by thesurgeon; is simple to put together and take apart as needed; and is madeup of components that are easy to fabricate and replicate in mass at lowcost.

As indicated hereinbefore, this desire includes being able to provide:(a) an acetabular cup assembly in which the bearing component can beeasily attached to the shell component in a large number of selectedorientations to provide the maximum degree of flexibility for thesurgeon using only a push-in force within some predefined range; (b) alocking mechanism for use in such assemblies (for interlocking the shelland insert), which allows the bearing component to be easily oriented,easily installed and be easily removed by the surgeon, if necessary,using only a pull-out force within some predefined range; and (c) anacetabular cup assembly in which the bearing component can be secured tothe shell component by a retention force (and associated means forinducing such force) that is strong enough to prevent rotation ordislocation of the bearing component from the shell component when thecup assembly is completed (after insertion of the bearing component intothe shell component in a desired orientation) and being used as intendedas a hip prosthesis device.

Furthermore, in view of the prior art discussed hereinabove, it would beparticularly desirable to provide a locking mechanism for an acetabularcup assembly which includes a retaining ring that is made from amaterial that is strong, easy to machine and does not require theperformance of the aforementioned wire shaping and/or heat treatmentring fabrication process steps.

Further yet, it is desirable to provide a locking mechanism for anacetabular cup assembly, that includes a retaining ring that is madefrom a material that allows the rings to be mass produced by, forexample, an injection molding process to realize objectives of beingable to minimize locking mechanism fabrication costs, assure consistencyin the locking mechanism fabrication process and assure the quality ofthe components produced by such processes, etc.

Further still, it would be desirable to provide an acetabular cupassembly and a locking mechanism therefore, for use in such assembly toretain the bearing component inside the shell component afterinstallation, which includes a retaining ring that is formed usingmaterials that exhibit consistent push-in and pull-out forces; andresult in assemblies that do not experience shell/insert toggle.

In view of the teachings of the incorporated Engelhardt et al. patent,which illustrates the present state of the art, it would be desirable toprovide a locking mechanism that prevents rotation of assemblycomponents and substantially eliminates motion between assemblycomponents without having to machine or otherwise form separate means(like Engelhardt's lugs) to prevent such rotation and/or other motion.

Finally, it would be desirable to provide processes per se forfabricating the aforementioned desirable locking mechanisms andretaining rings, particularly those locking mechanisms and retainingrings that are suitable for incorporation into acetabular cupassemblies.

SUMMARY OF THE INVENTION

In view of the foregoing, it is a general object of the invention toprovide an acetabular cup assembly in which the bearing component can beeasily attached to the shell component in a large number of selectedorientations to provide the maximum degree of flexibility for thesurgeon using only a push-in force within some predefined range.

It is a further object of the invention to provide a locking mechanismfor use in such assemblies (for interlocking the shell and insert),which allows the bearing component to be easily oriented, easilyinstalled and be easily removed by the surgeon, if necessary, using onlya pull-out force within some predefined range.

Still further, it is an object of the invention to provide an acetabularcup assembly in which the bearing component can be secured to the shellcomponent by a retention force (and associated means for inducing suchforce) that is strong enough to prevent rotation or dislocation of thebearing component from the shell component when the cup assembly iscompleted (after insertion of the bearing component into the shellcomponent in a desired orientation) and being used as intended as a hipprosthesis device.

Yet another object of the invention is to provide means for retaining apolymeric (or composite) bearing component (the insert) inside anacetabular metal shell without the use of attachment screws or metalliclock rings.

Furthermore, it is an object of the invention to provide a lockingmechanism for an acetabular cup assembly, including a retaining ringtherefore, that can be fabricated using a material that is strong, easyto machine and does not require the performance of the aforementionedwire shaping and/or heat treatment ring fabrication process steps.

Further still, it is an object of the invention to provide a lockingmechanism for an acetabular cup assembly, including a retaining ringtherefore, that can be fabricated using an injection molding process onproduction quantities to reduce the cost, assuring the consistency andquality of the components produced, etc.

Still another object of the invention is to provide an acetabular cupassembly and a locking mechanism therefore, for use in such assembly toretain the bearing component inside the shell component afterinstallation, which includes a retaining ring that is formed usingmaterials that exhibit consistent push-in and pull-out forces; andresult in assemblies that do not experience shell/insert toggle.

It is also an object of the invention to provide a locking mechanismthat prevents rotation of assembly components and substantiallyeliminates motion between assembly components without having to machineor otherwise form separate means intended to prevent such rotationand/or other motion.

Finally, it is an object of the invention to provide processes forfabricating the aforementioned desirable locking mechanisms andretaining rings.

According to one aspect of the invention, alternative materials havebeen identified for use in fabricating retaining rings, particularlyretaining rings used as part of locking mechanisms that secure thecomponents of an acetabular cup assembly.

One such material is PEEK, which is a member of the polyaryletherketonepolymer family. The polymer PEEK has excellent mechanical properties andmachinability. Evaluations of this material, discussed in more detailhereinafter in the Detailed Description of the invention, have shownthat PEEK retaining rings with tight tolerance can be easily machined tofit into the groove in the insert and the metal shell backing; and thatno rocking motion was noticed in the assembly (presumably due to thebetter dimension fit between the ring, insert and shell).

Composite materials, such as PEEK reinforced with carbon fiber, havealso been identified as being suitable for meeting the aforestatedobjectives.

The invention may best be appreciated by those skilled in the art byconsidering various aspects thereof to be set forth immediatelyhereinafter. In particular, one aspect of the invention is directed toan acetabular cup assembly for a femur ball, comprising: (a) an insertbearing component for receiving the femur ball; (b) an outer shellcomponent, for attachment to an acetabulum to replace a natural hipsocket, including a cavity for receiving the insert bearing componenttherein; and (c) a locking mechanism for interlocking the insert intothe outer shell, the locking mechanism comprising a retaining ring thatis fabricated at least in part using polyaryletherketone material.

According to a preferred embodiment of this first aspect of theinvention, the polyaryletherketone material is PEEK and the ring is madeentirely of PEEK (i.e., is a 100% PEEK ring). Furthermore, in accordancewith alternate embodiments of the invention, the PEEK may be reinforcedusing a material like carbon fiber.

According to another aspect of the invention, a prosthetic acetabularcup assembly for receiving a ball attached to a femur, comprises: (a) aninsert bearing component, including an inner bearing surface forreceiving the ball and an outer surface formed to include an arcuategroove therein; (b) an outer shell component for attachment to anacetabulum to replace a natural hip socket, the outer shell componentincluding an inner surface defining a cavity for receiving the insertbearing component therein, the inner surface of the outer shellcomponent being formed to include an arcuate groove therein at alocation that is axially aligned with the arcuate groove formed in theinsert bearing component; and (c) a locking mechanism that when locatedin the arcuate groove of the outer shell component will engage theinsert bearing component, upon insertion of the insert bearing componentinto the outer shell component, by extending into the arcuate groovelocated on the outer surface of the insert bearing component to therebyretain the insert bearing component inside the outer shell component,the locking mechanism comprising a retaining ring that is fabricated atleast in part using polyaryletherketone material (e.g., PEEK).

A further aspect of the invention is directed to a locking mechanism perse for interlocking components of an acetabular cup assembly, thelocking mechanism comprising a retaining ring that is fabricated atleast in part using polyaryletherketone material (like PEEK); togetherwith a reinforcing material (like carbon fiber). The locking mechanismis further defined, according to this aspect of the invention, toinclude a retaining ring formed (using the materials describedhereinabove) to simultaneously fit into grooves located in thecomponents being interlocked.

Further variants on (alternate embodiments of) this aspect of theinvention (directed to the locking mechanism per se) encompass, by wayof example and without limitation except as specifically recited in theclaims, the use of (as part of such mechanism) a closed retaining ring;a "split" (open) retaining ring; retaining rings that are circular inshape; retaining rings that have a polygon shape (such as penta shapedand hex shaped rings); retaining rings that are chamfered in any one ofa variety of ways; retaining rings formed to included any number oflobes; and/or rings combining any number of the above features with theobject of achieving push-in and pull-out forces within a predefinedrange, substantially eliminating cup assembly component motion, etc., asdiscussed hereinbefore.

Furthermore, according to this aspect of the invention (directed to thelocking mechanism apparatus per se) the retaining rings used may befabricated via a machining process using extruded polyaryletherketonestock; and as a preferred alternative, the rings are contemplated asbeing a product of an injection molding process.

Another aspect of the invention is directed to a process per se forfabricating a locking mechanism to secure components of an acetabularcup assembly, the assembly including an insert bearing component forreceiving a femur ball and an outer shell component, for attachment toan acetabulum to replace a natural hip socket, including a cavity forreceiving the insert bearing component therein, comprising the steps of:(a) forming a first arcuate groove on the outer surface of the insertbearing component; (b) forming a second arcuate groove on the innersurface of the outer shell component at a location that is axiallyaligned with the arcuate groove formed in the insert bearing component;and (c) fabricating a retaining ring for interlocking the insert intothe outer shell, the retaining ring being formed at least in part usingpolyaryletherketone. Alternative embodiments of this process contemplateutilizing a machining process to form the ring; and utilizing aninjection molding process to form the ring.

The locking mechanism fabrication process contemplated by this aspect ofthe invention further comprehends (again, by way of example withoutlimitation except as expressly recited in the claims) using PEEK to formthe retaining ring; forming the ring (according to one embodiment of theinvention) such that the finished ring, when located simultaneously inthe first arcuate groove and the second arcuate groove to therebyinterlock the insert and outer shell, has a finite number of contactpoints on both the insert and on the outer shell; forming the ring (inan alternate embodiment of the invention) such that the finished ring iscircular in shape; forming the retaining ring as a split ring; formingthe retaining ring as a closed ring; combining the polyaryletherketonewith a reinforcing material (such as carbon fiber), etc.

Yet another aspect of the invention is directed to a process forfabricating a retaining ring for an acetabular cup assembly thatincludes (a) an insert bearing component having an inner bearing surfacefor receiving the ball and an outer surface formed to include an arcuategroove therein and (b) an outer shell component for attachment to anacetabulum to replace a natural hip socket, the outer shell componentincluding an inner surface defining a cavity for receiving the insertbearing component therein, the inner surface of the outer shellcomponent being formed to include an arcuate groove therein at alocation that is axially aligned with the arcuate groove formed in theinsert bearing component, comprising the steps of: (a) creating a moldfor the retaining ring having a predefined shaped which allows the ring,when formed, to be inserted into the arcuate groove of the outer shellcomponent and simultaneously engage the insert bearing component, uponinsertion of the insert bearing component into the outer shellcomponent, by extending into the arcuate groove located on the outersurface of the insert bearing component; and (b) injecting apolyaryletherketone material into the mold.

Alternate embodiments of this aspect of the invention include processeswhere the polyaryletherketone is PEEK; forming the ring such that thefinished ring is circular in shape; forming the retaining ring as asplit ring; forming the retaining ring as a closed ring; combining thepolyaryletherketone with a reinforcing material (such as carbon fiber),etc.

Still another aspect of the invention is directed to a process forfabricating retaining rings used in acetabular cup assemblies forinterlocking the components thereof, comprising the steps of: (a)forming a mold to create retaining rings having a predetermined shapeenabling each such ring to extend simultaneously into a pair of grooves,each located in one of a pair of components being interlocked, usingonly a push-in force within a predefined range of push-in forces tocombine the components and the ring; and (b) injectingpolyaryletherketone material into the mold as part of an injectionmolding process to create the retaining rings having the predeterminedshape.

Furthermore, according to this aspect of the invention, thepredetermined shape is such that only a predetermined amount of pull-outforce within a predefined range of pull-out forces is required toseparate the combination of said pair of components and ring oncejoined.

Finally, certain other specific aspects of the invention are directed toa retaining ring per se, fabricated at least in part usingpolyaryletherketone material (preferably reinforced PEEK), where oneapplication of the ring is for use in an acetabular cup assembly; a PEEKretaining ring per se, used as part of a locking mechanism forinterlocking components of an acetabular cup assembly; and a compositePEEK/carbon fiber retaining ring per se, used as part of a lockingmechanism for interlocking components of an acetabular cup assembly.

The invention features locking mechanisms including retaining rings andretaining rings per se, made from materials that can be easily machined;and are suitable for use in injection molding processes to lower ringproduction costs, etc. These locking mechanisms and retaining rings areparticularly useful in acetabular cup assemblies.

Furthermore, the invention features acetabular cup assembliesincorporating the aforementioned component locking mechanisms and/orretaining rings; and process for fabricating locking mechanisms andretaining rings meeting the aforestated objectives.

Further still, the invention features acetabular cup assemblies in whichthe bearing component can be easily attached to the shell component in alarge number of selected orientations to provide the maximum degree offlexibility for the surgeon; locking mechanisms (including retainingrings) for use in such assemblies for interlocking the shell and insert,which allow the bearing component to be easily oriented, easilyinstalled and be easily removed by the surgeon; acetabular cupassemblies in which the bearing component can be secured to the shellcomponent by a retention force (and associated means for inducing suchforce) that is strong enough to prevent rotation or dislocation of thebearing component from the shell component when the cup assembly iscompleted, without the use of attachment screws or metallic lock rings;and acetabular cup assemblies that include locking mechanisms (whichfurther include retaining rings) formed using materials that exhibitconsistent push-in and pull-out forces, prevent rotation of assemblycomponents and substantially eliminate motion between assemblycomponents without having to machine or otherwise form separate meansintended to prevent such rotation and/or other motion.

These and other objects, embodiments and features of the presentinvention and the manner of obtaining them will become apparent to thoseskilled in the art, and the invention itself will be best understood byreference to the following Detailed Description read in conjunction withthe accompanying Drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 depicts an exploded view of a prosthetic acetabular cup assemblyin which the instant invention may be advantageously used.

FIG. 2 depicts a top view of a two versions of a circular Vitallium wireretaining ring; one version having six lobes as shown on the left handside of FIG. 2 and the other version having three lobes as shown on theright hand side of FIG. 2. Both rings are "closed" (i.e., form acontinuous loop).

FIG. 3 depicts a top view of a closed circular polyethylene retainingring (shown on the left hand side of FIG. 3); and an exemplary crosssectional view of the aforementioned ring showing an outside chamfer.

FIG. 4 depicts a top view of an open ("split") circular retaining ring,fabricated at least in part using a polyaryletherketone material (e.g.,PEEK), shown on the left hand side of FIG. 4; and an exemplary crosssectional view of the aforementioned ring indicating no chamfer.

FIG. 5 depicts a top view of an open ("split") circular retaining ring,fabricated at least in part using a polyaryletherketone material (shownon the left hand side of FIG. 5); and an exemplary cross sectional viewof the aforementioned ring indicating the ring is chamfered.

FIG. 6 depicts a top view of a closed penta shaped retaining ring,fabricated at least in part using a polyaryletherketone material.

FIG. 7 depicts a top view of three closed penta shaped retaining ringshaving varying inner diameters and "band widths" (defined as thedifference between the outer diameter and the inner diameter of thering), where each ring is again fabricated at least in part using apolyaryletherketone material.

FIG. 8 depicts a top view of a closed penta shaped retaining ring withchamfers, fabricated at least in part using a polyaryletherketonematerial (shown on the right hand side of FIG. 8); and an exemplarycross sectional view of the aforementioned ring depicting the chamfer(shown on the left hand side of FIG. 8).

FIG. 9 depicts a top view of a closed penta shaped retaining ring withinside circular chamfers having varying diameters (as shown in the tableincluded as part of FIG. 9), where the ring is fabricated at least inpart using a polyaryletherketone material. FIG. 9 also depicts anexemplary cross sectional view of the aforementioned ring depicting thechamfer.

FIG. 10 depicts a top view of a closed circular retaining ring with aninside chamfer, fabricated at least in part using a polyaryletherketonematerial (shown on the right hand side of FIG. 10); and an exemplarycross sectional view of the aforementioned ring depicting the chamfer(shown on the left hand side of FIG. 10).

FIG. 11 depicts a top view of a closed circular retaining ring with aninside chamfer that is penta shaped, fabricated at least in part using apolyaryletherketone material (shown on the right hand side of FIG. 11);and an exemplary cross sectional view of the aforementioned ringdepicting the chamfer (shown on the left hand side of FIG. 11).

FIG. 12 depicts a top view of a closed hex shaped retaining ring with aninside radial chamfer, where the ring is fabricated at least in partusing a polyaryletherketone material (shown on the right hand side ofFIG. 12); and an exemplary cross sectional view of the aforementionedring depicting the chamfer (shown on the left hand side of FIG. 12).

FIG. 13 depicts a top view of a closed hex shaped retaining ring with aninside radial chamfer, where the ring is fabricated at least in partusing a polyaryletherketone material (shown on the right hand side ofFIG. 13); and an exemplary cross sectional view of the aforementionedring depicting the chamfer (shown on the left hand side of FIG. 13).

DETAILED DESCRIPTION

The invention will now be described with reference to a set ofexperiments conducted on various acetabular cup component lockingmechanisms, including retaining rings fabricated using Vitallium wire,Ultra-High Molecular Weight Polyethylene (UHMWPE) andpolyaryletherketone material, to demonstrate by way of examplequantifiable advantages of using a polyaryletherketone, such as PEEK, inrealizing the aforestated objects of the invention. The experimentsconducted and results observed are in no way intended to limit the scopeor spirit of the invention which is intended to be limited only by theclaims appended hereto.

The object of the experiments conducted was to develop a suitableretaining ring for locking a composite acetabular cup (theaforementioned "insert" component), into an outer shell. The experimentswere conducted using Vitalock (TM) shells, commercially available fromthe assignee of the present invention. A 50 mm/28 mm P3 shell was usedfor this design. The insert used in combination with the shell had ano-ring type groove incorporated therein for locking the insert into theshell. The use of such a groove as part of a locking mechanism in anacetabular cup assembly is known in the prior art, as exemplified by theteachings of the incorporated reference where the bearing component isshown to include such groove (also referred to in the incorporatedreference and elsewhere herein as an "arcuate groove" which ispreferably axially aligned with a corresponding groove inside the shellcomponent into which the bearing component is inserted).

Furthermore, for the experiments conducted, it was assumed that theinsert had to be face loaded on its flange area; substantially allmotion between assembled parts had to be eliminated; and it was anobject of the experiments to find a locking mechanism and retaining ringfor which the push-in/pull-out forces of the cup assembly were withinindustry standards understood by those skilled in the art.

Reference should now be made to FIG. 1 which depicts a prostheticacetabular cup assembly 100 for a femur ball that includes insertbearing component 101 for receiving the femur ball; and outer shellcomponent 102 which may be attached to an acetabulum to replace anatural hip socket, with the depicted outer shell component 102including cavity 103 for receiving insert bearing component 101.

Insert bearing component 101 is further shown in FIG. 1 to include aninner bearing surface 104 for receiving the ball and an outer surface105 formed to include arcuate groove 106 therein. Inner surface 103 ofouter shell component 102 is also shown to include an arcuate groove(107) formed therein at a location that is axially aligned with arcuategroove 106 formed in insert bearing 101.

The instant invention focuses on the form and composition of lockingmechanisms that may be used to interlock acetabular cup assemblycomponents, such as insert bearing component 101 and outer shellcomponent 102 depicted in FIG. 1. An exemplary prior art mechanism usedfor this purpose (which sits, after assembly, simultaneously in arcuategrooves 106 and 107) is shown at 108 in FIG. 1, in the form of ametallic retaining ring wave washer.

A chronological development sequence ensued in which three differentring materials were researched and tested, Vitallium (TM), Ultra-HighMolecular Weight Polyethylene (UHMWPE), and a polyaryletherketonematerial, specifically, PEEK.

Reference should now be made to FIG. 2 which, as indicated hereinbefore,depicts a top view of a two versions of a circular Vitallium wireretaining ring; one version having six lobes (designated as the lobesbetween ring segments 200-1 to 200-2; 200-2 to 200-3; 200-3 to 200-4;200-4 to 200-5; 200-5 to 200-6; and 200-6 to 200-1), as shown on theleft hand side of FIG. 2 at 200; and the other version having threelobes (designated as the lobes between ring segments 201-1 to 201-2;201-2 to 201-3; and 201-3 to 201-1), as shown on the right hand side ofFIG. 2 at 201. Both rings are "closed" (i.e., form a continuous loop).

Vitallium rings, such as those depicted in FIG. 2 at 200 and 201, weredesigned and experiments conducted which verified Vitallium can be usedas a spring lock mechanism. However, the ability for Vitallium rings toretain their springing capability on a long term basis remains unknownand is a concern for a lock mechanism being employed in the human bodyas part of an acetabular cup assembly.

It was determined via the experiments conducted that Vitallium can beformed or cast for production quantities. Exemplary wire diameters usedin the experiments were 0.062" and 0.045". Fixtures were developed toform the parts; and samples were made for each lobe design shown in FIG.2 (i.e., for a rings shaped as shown in FIG. 2 at 200 and 201,respectively), for each of the aforementioned wire diameters.

Testing results for both the three and six lobe variations were similar.The 0.062" wire was to stiff (the wire was too thick); and the 0.045"wire was to sloppy (the wire was too thin).

Samples of 0.055" and 0.050" diameter wire were obtained and rings weretested. The further test results showed that although the wire diametersfit nicely into the grooves on the shell and insert; the shell/insertinterface was still too loose. A rocking motion was observed in theassembly due to the locking mechanism not functioning properly. Offurther significance was the fact that push-out strength was very high;in excess of 1,500 pounds, as indicated hereinbefore.

Reference should now be made to FIG. 3 which, as indicated hereinbefore,depicts a top view of a closed circular polyethylene retaining ring(shown on the left hand side of FIG. 3 at 300) and an exemplary crosssectional view of the aforementioned ring (depicted in FIG. 3 at 301)showing an outside chamfer, 302.

Rings made of polyethylene (like the exemplary retaining ring 300 shownin FIG. 3 which was fabricated using UHMWPE), were tested and were foundto be thin, dimensionally inconsistent and were not readily amenable formachining (i.e., machinablity was poor). Insertion force requirementswere low and a significant amount of shell/insert rocking was noted. Asa result of these experiments work on additional polyethylene rings wasstopped and a search for an alternate polymeric material lead to theconsideration of a polyaryletherketone material, in particular PEEK, asa material from which to fabricate a retaining ring.

It was determined in further experiments that polyaryletherketonematerial, in particular PEEK, can be easily machined. The furtherexperiments resulted in the rings depicted in FIGS. 4-13 beingfabricated and tested with good results being achieved for meeting theaforestated objectives of the invention. These ring designs andexperimental results will be set forth hereinafter to demonstrate thatlocking mechanisms and retaining rings for acetabular cup assemblies,fabricated in part using polyaryletherketone material, meet theaforementioned objectives.

Reference should now be made to FIG. 4 which, as indicated hereinbefore,depicts a top view of an open ("split") circular retaining ring 400,fabricated at least in part using a polyaryletherketone material (e.g.,PEEK), shown on the left hand side of FIG. 4; and an exemplary crosssectional view 401 of the aforementioned ring indicating no chamfer(indicated via reference numeral 402).

Experimental rings of the type depicted in FIG. 4 were fabricated andtested in a first experiment with variety of thicknesses ranging from0.054" to 0.058". All the rings were split with a small section removed,as shown at 403 in FIG. 4. Push-in forces experienced during this firstexperiment ranged from 30 kg to greater than 500 kg. Push-out forcesrequired exceeded 500 kg.

A second test performed on the type of ring depicted in FIG. 4, on threeadditional circular rings, varied from hand assembled to a push-in forcerequirement of 715 kg; push out force requirements varied from a readingto low to determine to 658 kg. These values were considered to be toohigh and further experimentation with PEEK retaining ring designcontinued with the type of ring depicted in FIG. 5.

As indicated hereinbefore, FIG. 5 depicts a top view of an open("split") circular retaining ring fabricated at least in part using apolyaryletherketone material (an example of such ring is shown at 500 onthe left hand side of FIG. 5); and an exemplary cross sectional view ofring 500, shown at 501 in FIG. 5, indicates ring 500 is chamfered. Thischamfer feature is depicted in cross sectional view 501 at 502; and isfurther depicted with reference to ring 500 at 503 (depicting an insidechamfer) and 504 (depicting an outside chamfer).

The performance of PEEK rings like ring 500 (with chamfers like chamfer503 and chamfer 504 added respectfully to the inside and outsidediameters of such circular rings), was compared with similar non-chamferPEEK rings with various band widths and thickness ranging from 0.060" to0.066".

Test results indicted circular PEEK retaining rings, with and withoutchamfers, had inconsistent push-in/push-out results and most of thetested assemblies had shell/insert toggle. It was apparent from thisexperiment that the chamfering alone was not enough to achieve thedesired performance requirements for retaining rings used in acetabularcup assemblies and that further modification would be needed.

A larger sample of twenty four circular PEEK rings were tested, bothchamfered and non-chamfered rings. All were hand assembled and veryloose with very high push out forces required.

A different concept for the PEEK rings was then tested. The design ofthe new ring, a top view of which is shown in FIG. 6 as exemplary ring600, was a closed penta shaped retaining ring fabricated at least inpart using a polyaryletherketone material. The penta shaped design whichgives five points of contact on the insert and five on the shell. Twosuch rings were fabricated and tested with the test results showingpush-in forces of 5 kg and 5.6 kg for the two tests respectively.Furthermore, the fit of the ring was good and a push-out force of 297kg. was measured.

Six additional penta rings were made with varying band widths. Three ofthese rings, 700, 701 and 702, are depicted in FIG. 7 which depicts atop view of the three rings. Each of the rings depicted in FIG. 7 is aclosed penta shaped retaining ring. Rings 700-702 having varying innerdiameters and band widths (examples of which are illustrated in FIG. 7).All of the depicted rings were hand assembled and fabricated at least inpart using a polyaryletherketone material for the experiments to beconducted; two of the rings were fabricated with inside chamfers.

Two push-in tests conducted on non-chamfered rings of the type depictedin FIG. 7, recorded required push-in forces of 7.7 kg and 11 kg. Allassembled parts had various degrees of toggling. The range of push-outfor non-chamfered rings was 240 lbs through 468 lbs. The push-out forcesfor the two inside chamfered rings were lower as expected, with one testyielding a required push-out force of 29 lbs.

Ring size and shape optimization experiments continued. A wide varietyof rings having were designed and tested, such as the closed chamferedpenta shaped ring 800 depicted in FIG. 8 (an example of the chamferbeing shown at 801). The right hand side of FIG. 8 depicts a top view ofring 800, which was fabricated at least in part using apolyaryletherketone material; and an exemplary cross sectional view 802of ring 800 (with the section being taken along line A--A cut throughring 800) is shown on the left hand side of FIG. 8. Chamfer 801 isillustrated as 803 and 804 in the cross section.

Reference should now be made to FIGS. 9-12 which depict several of theother types of rings that were designed and tested.

As indicated hereinbefore:

(1) FIG. 9 depicts a top view of a closed penta shaped retaining ring(shown as ring 900 in FIG. 9) with inside circular chamfers havingvarying diameters (as shown in table 901 included as part of FIG. 9),where the ring is fabricated at least in part using apolyaryletherketone material. FIG. 9 also depicts an exemplary crosssectional view 902 of ring 900 (with the section being taken along lineA--A cut through ring 900), depicting inside circular chamfers 903 and904.

(2) FIG. 10 depicts a top view of a closed circular retaining ring(1000) fabricated at least in part using a polyaryletherketone material,having an inside chamfer 1001 (with ring 1000 being shown on the righthand side of FIG. 10); and an exemplary cross sectional view 1002 ofring 1000 (with the section being taken along line A--A cut through ring1000), depicting inside chamfer 1001 at 1003 and 1004 in cross sectionalview 1002. Cross sectional view 1002 of ring 1000 is shown on the lefthand side of FIG. 10.

(3) FIG. 11 depicts a top view of a closed circular retaining ring(1100) fabricated at least in part using a polyaryletherketone material,with an inside chamfer 1101 that is penta shaped (with ring 1100 beingshown on the right hand side of FIG. 11); and an exemplary crosssectional view 1102 of ring 1100 (with the section being taken alongline A--A cut through ring 1100), depicting inside chamfer 1101 at 1103and 1104 in cross sectional view 1102. Cross sectional view 1102 of ring1100 is shown on the left hand side of FIG. 11.

(4) FIG. 12 depicts a top view of a closed hex shaped retaining ring(1200) with an inside radial chamfer 1201, where ring 1200 (shown on theright hand side of FIG. 12) is fabricated at least in part using apolyaryletherketone material; and an exemplary cross sectional view 1202of ring 1200 (shown on the left hand side of FIG. 12), depicting insideradial chamfer 1201 at 1203 and 1204.

A total of 36 rings were tested with the results improving using thering designs depicted in FIGS. 9-12. Most push-in forces observed werevery good, in the range of 13 kg to 20 kg. Different sizes and shapeshad varied degrees of toggle, with push-out forces ranging from 2 kg.through 129 kg.

The experiments discussed hereinabove helped focus attention on thepenta and hex shaped rings.

Several more rings (all fabricated using PEEK), with different outsideand inside diameters, with two different band widths, were tested. Mostassemblies were very tight depending on the outside and insidedimensions. The higher band widths seemed to increase the push-in andpull-out forces slightly. Push-out forces observed in the experimentsconducted were very good, ranging from 20 kg to 163 kg.

The most promising data observed was for a hex shaped retaining ring(again fabricated using PEEK), having an outer diameter of 1.640" and aninner diameter of 1.365".

Such a ring is depicted in FIG. 13 where, as indicated hereinbefore, atop view of a closed hex shaped retaining ring 1300 with an insideradial chamfer 1301 is depicted. Ring 1300, is fabricated at least inpart using a polyaryletherketone material and is shown on the right handside of FIG. 13. An exemplary cross sectional view (1302) of ring 1300,depicting chamfer 1301 at 1303 and 1304, is shown on the left hand sideof FIG. 13.

For a ring of the type illustrated by ring 1300, with a 0.060" bandwidth, push-in forces of 23 kg, 21 kg and 20 kg were observed in threetests performed. Push-out forces observed were 82 kg, 66 kg and 163 kg.

For a 0.070" band width (with two tests performed), the push-in forceswere 27 kg and 32 kg; and push-out forces were 66 kg and 140 kg.

As a result of the experiments described hereinabove, it was concludedthat penta and hex shaped rings made at least in part using apolyaryletherketone material (like PEEK) were very well suited for usein acetabular cup assemblies.

It was further concluded after additional experimentation that ringsmade using composite materials, such as PEEK reinforced with carbonfiber, are particularly well suited for meeting the aforestatedobjectives of then invention, including, without limitation, being ableto fabricate such rings in mass using well known injection moldingprocesses, etc. More particularly, it was found that by adding areinforcing material to the PEEK matrix the composite ring wasstrengthened and exhibited increased rigidity when compared with ringsthat were not reinforced.

According to the invention, an exemplary process for fabricating alocking mechanism to secure components of an acetabular cup assembly,where the assembly includes an insert bearing component for receiving afemur ball and an outer shell component, for attachment to an acetabulumto replace a natural hip socket, including a cavity for receiving theinsert bearing component therein, comprises the steps of: (a) forming afirst arcuate groove on the outer surface of the insert bearingcomponent; (b) forming a second arcuate groove on the inner surface ofthe outer shell component at a location that is axially aligned with thearcuate groove formed in the insert bearing component; and (c)fabricating a retaining ring for interlocking the insert into the outershell, the retaining ring being formed at least in part usingpolyaryletherketone.

Further details of this process include utilizing a machining process toform the ring or alternatively utilizing an injection molding process toform the ring.

According to a preferred embodiment of the invention, thepolyaryletherketone used in the aforementioned process is PEEK; and thefinished ring (preferably 100% PEEK), when located simultaneously in thefirst arcuate groove and the second arcuate groove (to thereby interlockthe insert and outer shell), has a finite number of contact points onboth the insert and on the outer shell. According to alternateembodiments of the invention the polyaryletherketone used is combinedwith a reinforcing material, like carbon fiber, when added strength isrequired.

The invention also contemplates a process for fabricating a retainingring for an acetabular cup assembly that includes (a) an insert bearingcomponent having an inner bearing surface for receiving the ball and anouter surface formed to include an arcuate groove therein and (b) anouter shell component for attachment to an acetabulum to replace anatural hip socket, the outer shell component including an inner surfacedefining a cavity for receiving the insert bearing component therein,the inner surface of the outer shell component being formed to includean arcuate groove therein at a location that is axially aligned with thearcuate groove formed in the insert bearing component, comprising thesteps of: (a) creating a mold for the retaining ring having a predefinedshaped which allows the ring, when formed, to be inserted into thearcuate groove of the outer shell component and simultaneously engagethe insert bearing component, upon insertion of the insert bearingcomponent into the outer shell component, by extending into the arcuategroove located on the outer surface of the insert bearing component; and(b) injecting a polyaryletherketone material into the mold.

What has been described in detail hereinabove are acetabular cupassemblies, locking mechanisms, retaining rings and processes forfabricating these devices, which meet all of the aforestated objectives.As previously indicated, those skilled in the art will recognize thatthe foregoing description has been presented for the sake ofillustration and description only. It is not intended to be exhaustiveor to limit the invention to the precise form disclosed, and obviouslymany modifications and variations are possible in light of the aboveteaching.

The embodiments and examples set forth herein were presented in order tobest explain the principles of the instant invention and its practicalapplication to thereby enable others skilled in the art to best utilizethe instant invention in various embodiments and with variousmodifications as are suited to the particular use contemplated.

In view of the above it is, therefore, to be understood that the claimsappended hereto are intended to cover all such modifications andvariations which fall within the true scope and spirit of the invention.

What is claimed is:
 1. An acetabular cup assembly for a femur ball,comprising:(a) an insert bearing component for receiving the femur ball;(b) an outer shell component, for attachment to an acetabulum to replacea natural hip socket, including a cavity for receiving said insertbearing component therein; and (c) a locking mechanism for interlockingsaid insert into said outer shell said locking mechanism comprising aretaining ring that is fabricated at least in part usingpolyaryletherketone material.
 2. Apparatus as set forth in claim 1wherein said polyaryletherketone material is PEEK.
 3. Apparatus as setforth in claim 2 wherein said retaining ring further comprises areinforcing material that combined with said PEEK reinforces the ring.4. Apparatus as set forth in claim 3 wherein said reinforcing materialcomprises carbon fiber.
 5. Apparatus as set forth in claim 1 whereinsaid retaining ring further comprises a reinforcing material thatcombined with said polyaryletherketone material reinforces the ring. 6.Apparatus as set forth in claim 5 wherein said reinforcing materialcomprises carbon fiber.
 7. An prosthetic acetabular cup assembly forreceiving a ball attached to a femur, the assembly comprising:(a) aninsert bearing component, including an inner bearing surface forreceiving said ball and an outer surface formed to include an arcuategroove therein; (b) an outer shell component for attachment to anacetabulum to replace a natural hip socket, the outer shell componentincluding an inner surface defining a cavity for receiving said insertbearing component therein, the inner surface of said outer shellcomponent being formed to include an arcuate groove therein at alocation that is axially aligned with the arcuate groove formed in saidinsert bearing component; and (c) a locking mechanism that when locatedin the arcuate groove of the outer shell component will engage theinsert bearing component, upon insertion of the insert bearing componentinto the outer shell component, by extending into the arcuate groovelocated on the outer surface of the insert bearing component to therebyretain the insert bearing component inside the outer shell component,said locking mechanism comprising a retaining ring that is fabricated atleast in part using polyaryletherketone material.
 8. Apparatus as setforth in claim 7 wherein said polyaryletherketone material is PEEK. 9.Apparatus as set forth in claim 8 wherein said retaining ring furthercomprises a reinforcing material that combined with said PEEK reinforcesthe ring.
 10. Apparatus as set forth in claim 9 wherein said reinforcingmaterial comprises carbon fiber.
 11. Apparatus as set forth in claim 7wherein said retaining ring further comprises a reinforcing materialthat combined with said polyaryletherketone material reinforces thering.
 12. Apparatus as set forth in claim 11 wherein said reinforcingmaterial comprises carbon fiber.
 13. A locking mechanism forinterlocking components of an acetabular cup assembly, said lockingmechanism comprising a retaining ring that is fabricated at least inpart using polyaryletherketone material.
 14. Apparatus as set forth inclaim 13 wherein said polyaryletherketone material is PEEK. 15.Apparatus as set forth in claim 14 wherein said retaining ring furthercomprises a reinforcing material that combined with said PEEK reinforcesthe ring.
 16. Apparatus as set forth in claim 15 wherein saidreinforcing material comprises carbon fiber.
 17. Apparatus as set forthin claim 13 wherein said retaining ring further comprises a reinforcingmaterial that combined with said polyaryletherketone material reinforcesthe ring.
 18. Apparatus as set forth in claim 17 wherein saidreinforcing material comprises carbon fiber.
 19. Apparatus as set forthin claim 13 wherein said retaining ring is formed to simultaneously fitinto grooves located in the components being interlocked.
 20. Apparatusas set forth in claim 13 wherein said retaining ring is a closed ring.21. Apparatus as set forth in claim 13 wherein said retaining ring is asplit ring.
 22. Apparatus as set forth in claim 13 wherein saidretaining ring is circular.
 23. Apparatus as set forth in claim 22wherein said retaining ring includes an inside chamfer.
 24. Apparatus asset forth in claim 22 wherein said retaining ring includes an outsidechamfer.
 25. Apparatus as set forth in claim 22 wherein said retainingring includes a plurality of inner diameter lobes.
 26. Apparatus as setforth in claim 22 wherein said retaining ring includes an insidecircular chamfer.
 27. Apparatus as set forth in claim 22 wherein saidretaining ring has an inside chamfer-penta shape.
 28. Apparatus as setforth in claim 13 wherein said retaining ring has a polygon shape. 29.Apparatus as set forth in claim 28 wherein said retaining is pentashaped.
 30. Apparatus as set forth in claim 29 wherein said retainingring is chamfered.
 31. Apparatus as set forth in claim 29 wherein saidretaining ring includes an inside radial chamfer.
 32. Apparatus as setforth in claim 28 wherein said retaining ring is hex shaped. 33.Apparatus as set forth in claim 32 wherein said retaining ring includesan inside radial chamfer.
 34. Apparatus as set forth in claim 13 whereinthe retaining ring that is fabricated at least in part usingpolyaryletherketone material is machined from extrudedpolyaryletherketone stock.
 35. Apparatus as set forth in claim 13wherein the retaining ring that is fabricated at least in part usingpolyaryletherketone material is the product of an injection moldingprocess.
 36. A process for fabricating a locking mechanism to securecomponents of an acetabular cup assembly, said assembly including aninsert bearing component for receiving a femur ball and an outer shellcomponent, for attachment to an acetabulum to replace a natural hipsocket, including a cavity for receiving said insert bearing componenttherein, comprising the steps of:(a) forming a first arcuate groove onthe outer surface of said insert bearing component; (b) forming a secondarcuate groove on the inner surface of said outer shell component at alocation that is axially aligned with the arcuate groove formed in saidinsert bearing component; and (c) fabricating a retaining ring forinterlocking said insert into said outer shell, said retaining ringbeing formed at least in part using polyaryletherketone.
 37. A processas set forth in claim 36 wherein said step of fabricating furthercomprises the step of utilizing a machining process to form said ring.38. A process as set forth in claim 36 wherein said step of fabricatingfurther comprises the step of utilizing an injection molding process toform said ring.
 39. A process as set forth in claim 36 wherein saidpolyaryletherketone is PEEK.
 40. A process as set forth in claim 36further comprising the step of forming said ring such that the finishedring, when located simultaneously in said first arcuate groove and saidsecond arcuate groove to thereby interlock said insert and outer shell,has a finite number of contact points on both the insert and on theouter shell.
 41. A process as set forth in claim 36 comprising the stepof forming said ring such that the finished ring is circular in shape.42. A process as set forth in claim 36 further comprising the step offorming said retaining ring as a split ring.
 43. A process as set forthin claim 36 further comprising the step of forming said retaining ringas a closed ring.
 44. A process as set forth in claim 36 furthercomprising the step of combining said polyaryletherketone with areinforcing material.
 45. A process as set forth in claim 44 whereinsaid reinforcing material is carbon fiber.
 46. A retaining ring orinterlocking components of an acetabular cup assembly, said ringfabricated at least in part using polyaryletherketone material. 47.Apparatus as set forth in claim 46 wherein said polyaryletherketonematerial is PEEK.
 48. Apparatus as set forth in claim 47 wherein saidretaining ring further comprises a reinforcing material that combinedwith said polyaryletherketone material reinforces the ring. 49.Apparatus as set forth in claim 48 wherein said material added tostrengthen said polymer is carbon fiber.
 50. Apparatus as set forth inclaim 46 wherein said retaining ring is used in an acetabular cupassembly.
 51. A PEEK retaining ring used as part of a locking mechanismfor interlocking components of an acetabular cup assembly.
 52. Acomposite PEEK/carbon fiber retaining ring used as part of a lockingmechanism for interlocking components of an acetabular cup assembly.